Fuel level sensors are used to detect the amount of stored fuel remaining in a fuel tank, and may perform this detection in a variety of manners. However, if a fuel level sensor does not operate normally, refuel timings may be missed. Accordingly, when a fuel level sensor fails, the fuel sensor must be promptly repaired or the like.
In one technique for diagnosing a failure in a fuel level sensor, the fuel level sensor is determined to be faulty if a change in the output of the fuel level sensor does not exceed a predetermined value when a predetermined amount of fuel is consumed.
In certain cases, when the fuel level sensor detects the movement of a float that floats in the fuel inside the tank, there are dead zones when the tank is full or empty. In these dead zones, the output of the fuel level sensor does not change according to the remaining amount of fuel.
If the tank is repeatedly refueled with smalls amount of fuel in these dead zones or an intermediate region such that the change amount in the fuel level sensor output does not exceed the predetermined value, the cumulative amount of consumed fuel may exceed the failure threshold before the fuel level sensor outputs the predetermined amount of change. In this case, even if the fuel level sensor is operating normally, the fuel level sensor may be determined to be faulty. Refer to, for example, JP 2007-010574 A and JP 2014-009597 A.